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1
Barr, D. J. S., and N. L. Désaulniers. "The flagellar apparatus in zoospores of Phytophthora, Pythium, and Halophytophthora." Canadian Journal of Botany 70, no. 11 (November 1, 1992): 2163–69. http://dx.doi.org/10.1139/b92-267.
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The flagellar apparatuses of 14 species of Phytophthora, 2 of Halophytophthora, and 4 of Pythium are compared in the transmission electron microscope. Except for Phytophthora infestans and Phytophthora mirabilis there were no significant differences in fine structure morphology. There are six flagellar roots: a ribbed triplet consisting of three main microtubules and secondary microtubules; an anterior doublet; a multistranded, band-shaped root of five to nine microtubules; a posterior root of two to four microtubules; and roots consisting of arrays of cytoplasmic microtubules and nuclear-associated microtubules. In P. infestans and P. mirabilis the multistranded root is missing, the posterior root contains five or six microtubules, and the anterior ribbed root contains four main microtubules. The transitional zones in all species are similar. The relationship of the Pythiaceae with other Oomycetes is discussed. Key words: taxonomy, phytogeny, cytology, Oomycetes, Pythiaceae.
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Weiland, Jerry E., Carolyn F. Scagel, Niklaus J. Grünwald, E. Anne Davis, Bryan R. Beck, Zachary S. L. Foster, and Valerie J. Fieland. "Soilborne Phytophthora and Pythium Diversity From Rhododendron in Propagation, Container, and Field Production Systems of the Pacific Northwest." Plant Disease 104, no. 6 (June 2020): 1841–50. http://dx.doi.org/10.1094/pdis-08-19-1672-re.
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Rhododendron root rot is a severe disease that causes significant mortality in rhododendrons. Information is needed about the incidence and identity of soilborne Phytophthora and Pythium species causing root rot in Pacific Northwest nurseries in order to better understand the disease etiology and to optimize disease control strategies. The last survey focusing solely on soilborne oomycete pathogens in rhododendron production was conducted in 1974. Since then, advances in pathogen identification have occurred, new species may have been introduced, pathogen communities may have shifted, and little is known about Pythium species affecting this crop. Therefore, a survey of root-infecting Phytophthora and Pythium species was conducted at seven nurseries from 2013 to 2017 to (i) document the incidence of root rot damage at each nursery and stage of production, (ii) identify soilborne oomycetes infecting rhododendron, and (iii) determine whether there are differences in pathogen diversity among nurseries and production systems. Rhododendrons from propagation, container, and field systems were sampled and Phytophthora and Pythium species were isolated from the roots and collar region. Root rot was rarely evident in propagation systems, which were dominated by Pythium species. However, severe root rot was much more common in container and field systems where the genus Phytophthora was also more prevalent, suggesting that Phytophthora species are the primary cause of severe root rot and that most contamination by these pathogens comes in after the propagation stage. In total, 20 Pythium species and 11 Phytophthora species were identified. Pythium cryptoirregulare, Pythium aff. macrosporum, Phytophthora plurivora, and Phytophthora cinnamomi were the most frequently isolated species and the results showed that Phytophthora plurivora has become much more common than in the past. Phytophthora diversity was also greater in field systems than in propagation or container systems. Risks for Phytophthora contamination were commonly observed during the survey and included placement of potting media in direct contact with field soil, the presence of dead plants that could serve as continuous sources of inoculum, and the presence of excess water as a result of poor drainage, overirrigation, or malfunctioning irrigation equipment. In the past, research on disease development and root rot disease control in rhododendron focused almost exclusively on Phytophthora cinnamomi. More research is needed on both of these topics for the other root-infecting species identified in this survey.
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Feng, Wenzhuo, Ayaka Hieno, Mikio Kusunoki, Haruhisa Suga, and Koji Kageyama. "LAMP Detection of Four Plant-Pathogenic Oomycetes and Its Application in Lettuce Fields." Plant Disease 103, no. 2 (February 2019): 298–307. http://dx.doi.org/10.1094/pdis-05-18-0858-re.
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In Kagawa Prefecture, Japan, the pathogens Phytophthora pseudolactucae, Pythium irregulare, Pythium uncinulatum, and Pythium spinosum have caused huge losses in lettuce production. We used loop-mediated isothermal amplification (LAMP) to analyze soil and plants in lettuce fields for the presence of these four pathogens. To develop an effective on-site detection method, we contrasted the Plant-LAMP and Plant Culture-LAMP procedures for plant samples, and five soil DNA extraction methods for soil samples. Plant-LAMP and a Soil DNA Isolation kit were selected to analyze three fields for the pathogen species present, infected sites, and level of soil contamination. We found that the same wilting symptoms could be caused by Phytophthora or Pythium, or a mixture of species from both genera. Ph. pseudolactucae infects the pith of the lettuce in aboveground parts, whereas Pythium spp. mainly infect roots. Ph. pseudolactucae and Py. uncinulatum caused disease more frequently than the other two pathogens. Furthermore, not all of the pathogens existed in the soil near infected lettuce plants. Therefore, the LAMP method can be used to diagnose pathogenic oomycetes in the field, and will be useful in the development of control strategies in lettuce production.
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Zahid, M. I., G. M. Gurr, A. Nikandrow, W. J. Fulkerson, and H. I. Nicol. "Pathogenicity of root and stolon-colonising fungi to white clover." Australian Journal of Experimental Agriculture 41, no. 6 (2001): 763. http://dx.doi.org/10.1071/ea00197.
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Fungi isolated from white clover plants growing in dairy pastures in northern New South Wales and south-eastern Queensland were tested for their pathogenicity to seedlings, excised stolons and mature white clover plants. Thirty out of 65 isolates tested, including species of Fusarium, Phytophthora, Pythium, Rhizoctonia, Phoma, Codinaea, Gliocladium, Microsphaeropsis, Trichoderma, Nectria and Macrophomina, were pathogenic to white clover roots in vitro. Ten of the fungi, including the genera Alternaria, Colletotrichum, Drechslera, Fusarium, Phoma, Macrophomina, Phomopsis and Rhizoctonia, caused stolon rot symptoms. Of the 23 fungi tested on seedlings and mature white clover plants Phytophthora megasperma, Phoma nebulosa and Pythium irregulare were the most pathogenic to both seedlings and mature plants. Root rot and plant growth suppression was more severe in pot tests using field soil compared with pasteurised potting mix. Novel methods are described for testing pathogenicity to excised stolons.
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Koike, S. T., and Frank N. Martin. "First Report of Phytophthora Root Rot Caused by Phytophthora cryptogea on Spinach in California." Plant Disease 94, no. 1 (January 2010): 131. http://dx.doi.org/10.1094/pdis-94-1-0131b.
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In 2006 and 2007, commercially grown spinach (Spinacia oleracea) in California's coastal Salinas Valley (Monterey County) was affected by an unreported root rot disease. Disease was limited to patches along the edges of fields. Affected plants were stunted with chlorotic older leaves. As disease progressed, most of the older foliage first wilted and then turned tan and dry; youngest leaves remained green but were stunted and leathery in texture. Plants most severely affected died. Symptoms on roots were mostly restricted to the distal portion of the root system, where feeder roots and the main taproot turned black. Isolations from root lesions consistently resulted in the recovery of a Phytophthora sp. The isolates were heterothallic, and on the basis of morphological and cytochrome oxidase 2 gene sequence data (GenBank Accession No. GQ984233), the pathogen was identified as Phytophthora cryptogea. To evaluate pathogenicity, individual inocula of four isolates were prepared by incubating colonized 6-mm-diameter V8 agar plugs in filtered soil extract for 2 days at 20°C to induce sporangia production. These cultures were then chilled at 4°C for 20 min and returned to room temperature for 1 h to induce zoospore release (4). Four-week-old spinach plants (cv. Bolero) were uprooted, soaked in suspensions of 1.0 × 105 zoospores/ml for 10 min, and repotted. After treatment, pots were placed in shallow trays of water for 24 h to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 9 days, inoculated plants showed foliar wilting and chlorosis similar to that observed in the field; after 13 days, roots were examined and found to show the black necrosis as seen in the field. P. cryptogea was isolated from all inoculated plants. Control spinach plants, treated with soil extract only, did not develop disease. This experiment was completed two times and the results were similar. To our knowledge, this is the first report of Phytophthora root rot of spinach caused by P. cryptogea in California. This finding is significant because spinach in California is subject to root rots caused by three other pathogens (Fusarium oxysporum, Pythium spp., and Rhizoctonia solani) (1); symptoms from these root rots are very similar to those caused by P. cryptogea, thereby complicating diagnosis. This pathogen has been documented on spinach in Germany and Sweden (2,3). References: (1) S. T. Koike et al. Vegetable Diseases: A Color Handbook. Manson Publishing LtD. London, 2007. (2) H. Krober and E.-O. Beckmann. Phytopathol. Z. 78:160, 1973. (3) M. Larsson and J. Olofsson. Plant Pathol. 43:251, 1994. (4) S. A. Tjosvold et al. Plant Dis. 93:371, 2009.
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Raftoyannis, Yannis, and Michael W. Dick. "Zoospore encystment and pathogenicity of Phytophthora and Pythium species on plant roots." Microbiological Research 161, no. 1 (January 2006): 1–8. http://dx.doi.org/10.1016/j.micres.2005.04.003.
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Olson, J. D., J. P. Damicone, and B. A. Kahn. "Identification and Characterization of Isolates of Pythium and Phytophthora spp. from Snap Beans with Cottony Leak." Plant Disease 100, no. 7 (July 2016): 1446–53. http://dx.doi.org/10.1094/pdis-06-15-0662-re.
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Cottony leak is an important disease of snap bean in Oklahoma and nearby states. Oomycete pathogens isolated from diseased pods collected from commercial fields and research plots consisted of both Pythium spp. (n = 131) and Phytophthora spp. (n = 46). Isolates were identified to species by morphological characteristics and by sequencing a portion of the internal transcribed spacer region of representative isolates. The most common Pythium spp. were Pythium ultimum var. ultimum; Pythium ‘group HS’, a self-sterile form of P. ultimum that produces hyphal swellings in lieu of sporangia (n = 74); and P. aphanidermatum (n = 50). Phytophthora spp. included Phytophthora drechsleri (n = 41) and P. nicotianae (n = 5). Nearly all of the isolates (95%) and all species were pathogenic on detached pods but Pythium ultimum var. ultimum and Pythium ‘group HS’ were most aggressive. Phytophthora drechsleri was most aggressive on seedlings, causing preemergence damping off and seed rot. Pythium ultimum var. ultimum, Pythium ‘group HS’, and P. aphanidermatum were intermediate in virulence to seedlings, causing root rot, stunting, and limited postemergence damping off. Phytophthora nicotianae and Pythium diclinum (n = 4) were not pathogenic on seedlings. Most (87%) isolates were sensitive to metalaxyl-M (concentration that caused a 50% reduction in mycelial growth [EC50] < 1 μg/ml) and the rest were intermediate in sensitivity (EC50 > 1 to < 100 μg/ml). Phytophthora drechsleri was the most sensitive species (EC50 = 0.06 μg/ml) compared with Pythium aphanidermatum, which was least sensitive (EC50 = 1.3 μg/ml). Cottony leak is a disease complex caused by several oomycete species that should include Phytophthora drechsleri, a newly reported pathogen of snap bean in the United States.
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Alejandro Rojas, J., Janette L. Jacobs, Stephanie Napieralski, Behirda Karaj, Carl A. Bradley, Thomas Chase, Paul D. Esker, et al. "Oomycete Species Associated with Soybean Seedlings in North America—Part I: Identification and Pathogenicity Characterization." Phytopathology® 107, no. 3 (March 2017): 280–92. http://dx.doi.org/10.1094/phyto-04-16-0177-r.
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Oomycete pathogens are commonly associated with soybean root rot and have been estimated to reduce soybean yields in the United States by 1.5 million tons on an annual basis. Limited information exists regarding the frequency and diversity of oomycete species across the major soybean-producing regions in North America. A survey was conducted across 11 major soybean-producing states in the United States and the province of Ontario, Canada. In 2011, 2,378 oomycete cultures were isolated from soybean seedling roots on a semiselective medium (CMA-PARPB) and were identified by sequencing of the internal transcribed spacer region of rDNA. Sequence results distinguished a total of 51 Pythium spp., three Phytophthora spp., three Phytopythium spp., and one Aphanomyces sp. in 2011, with Pythium sylvaticum (16%) and P. oopapillum (13%) being the most prevalent. In 2012, the survey was repeated, but, due to drought conditions across the sampling area, fewer total isolates (n = 1,038) were collected. Additionally, in 2012, a second semiselective medium (V8-RPBH) was included, which increased the Phytophthora spp. isolated from 0.7 to 7% of the total isolates. In 2012, 54 Pythium spp., seven Phytophthora spp., six Phytopythium spp., and one Pythiogeton sp. were recovered, with P. sylvaticum (14%) and P. heterothallicum (12%) being recovered most frequently. Pathogenicity and virulence were evaluated with representative isolates of each of the 84 species on soybean cv. Sloan. A seed-rot assay identified 13 and 11 pathogenic species, respectively, at 13 and 20°C. A seedling-root assay conducted at 20°C identified 43 species as pathogenic, having a significantly detrimental effect on the seedling roots as compared with the noninoculated control. A total of 15 species were pathogenic in both the seed and seedling assays. This study provides a comprehensive characterization of oomycete species present in soybean seedling roots in the major production areas in the United States and Ontario, Canada and provides a basis for disease management and breeding programs.
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Sánchez-Hernández, M. E., A. Ruiz-Dávila, and A. Trapero-Casas. "First Report of Phytophthora megasperma and Pythium irregulare As Olive Tree Root Pathogens." Plant Disease 81, no. 10 (October 1997): 1216. http://dx.doi.org/10.1094/pdis.1997.81.10.1216b.
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Several species of the genus Phytophthora are associated with root rot and trunk cankers in olive trees (Olea europaea L.). Among them, Phytophthora megasperma has been cited as being associated with olive root rots in Greece (1). Unidentified species of Pythium and Phytophthora have also been associated with olive tree root rots in the United States. However, the status of P. megasperma and Pythium spp. as olive tree root pathogens has remained unclear. Following a 5-year period of severe drought in southern Spain, autumn-winter rainfall rates in 1996 to 1997 steadily increased in both quantity and frequency. Under these unusually wet conditions, olive trees remained waterlogged for several months. During this period, we observed foliar wilting, dieback, and death of young trees, and later found extensive root necrosis. In 46 of 49 affected plantations surveyed, P. megasperma was consistently isolated from the rotted rootlets, particularly in young (<1- to 10-year-old trees) plantations. This fungus was not detected on plant material affected by damping-off from several Spanish olive tree nurseries. The opposite situation occurred with P. irregulare. This species was not associated with rotted rootlets in the field. In contrast, it was consistently isolated from necrotic rootlets from young olive plants affected by damping-off. These plants were grown in a sand-lime-peat soil mixture under greenhouse conditions and showed foliar wilting and extensive necrosis of the root systems. Pathogenicity tests were conducted with several isolates of P. megasperma and P. irregulare on 6-month-old rooted cuttings of olive, under both weekly watering and waterlogged conditions. Under waterlogged conditions, both fungal species produced extensive root necrosis 2 weeks after inoculation that resulted in wilting of the aerial parts and rapid plant death. Waterlogged control plants remained without foliar symptoms but a low degree of root necrosis was recorded. In addition, under weekly watering conditions, plants inoculated with either species showed some degree of root rot but foliar symptoms were not evident. No differences in pathogenicity were observed within the Phytophthora or Pythium isolates. Reference: (1) H. Kouyeas and A. Chitzanidis. Ann. Inst. Phytopathol. Benaki 8:175, 1968.
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Puertolas, Alexandra, Peter J. M. Bonants, Eric Boa, and Steve Woodward. "Application of Real-Time PCR for the Detection and Quantification of Oomycetes in Ornamental Nursery Stock." Journal of Fungi 7, no. 2 (January 27, 2021): 87. http://dx.doi.org/10.3390/jof7020087.
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Numerous Phytophthora and Pythium disease outbreaks have occurred in Europe following inadvertent introduction of contaminated ornamental plants. Detection and identification of pathogens are crucial to reduce risks and improve plant biosecurity in Europe and globally. Oomycete diversity present in roots and compost was determined in 99 hardy woody plants bought from nurseries, retailers and internet sellers, using both isolations and molecular analyses. Oomycete DNA was quantified using real-time PCR of environmental DNA from the plants using three loci: ITS, trnM-trnP-trnM and atp9-nad9. At least one oomycete species was isolated from 89.9% of plants using classical techniques. In total, 10 Phytophthora spp., 17 Pythium spp. and 5 Phytopythium spp. were isolated. Oomycetes were isolated from 86% of asymptomatic plants, but real-time PCR demonstrated that oomycetes were associated with all plants tested. More oomycete DNA occurred in composts in comparison with roots and filters from baiting water (a mean of 7.91 ng g−1, 6.55 × 10−1 ng g−1 and 5.62 × 10−1 ng g−1 of oomycete DNA detected in compost with ITS, trnM and atp9 probes, respectively); the ITS probe detected the highest quantities of oomycete DNA. No significant differences were found in quantities of oomycete DNA detected using real-time PCR in plants purchased online or from traditional retailers.
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Bryla, David R., Robert G. Linderman, and Wei Q. Yang. "Incidence of Phytophthora and Pythium Infection and the Relation to Cultural Conditions in Commercial Blueberry Fields." HortScience 43, no. 1 (February 2008): 260–63. http://dx.doi.org/10.21273/hortsci.43.1.260.
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Fifty-five commercial blueberry (Vaccinium spp.) fields were sampled in northwest Oregon in 2001 to determine the incidence of Phytophthora and Pythium root rot pathogens and identify cultural factors that increase the probability of developing infection. Phytophthora was detected in 24% and Pythium was detected in 85% of the fields sampled. The only species of Phytophthora identified in the study was P. cinnamomi. Root infection by P. cinnamomi was significantly related to cultivar with incidence observed more frequently than expected in ‘Duke’ and ‘Bluecrop’. Both blueberry cultivars are two of the most popular grown in the region, representing 42% of the fields in this survey and ≈46% of the total area planted in Oregon. Two other cultivars found infected by P. cinnamomi were ‘Rubel’ and ‘Briggitta Blue’, together accounting for an additional 24% of the fields surveyed. Phytophthora was not detected in fields planted with ‘Berkeley’, ‘Bluejay’, ‘Bluetta’, ‘Darrow’, ‘Earliblue’, ‘Elliott’, and ‘Powderblue’, each of which represented only 2% to 7% of the fields surveyed. Pythium spp. were identified to genus only, but one or more species of Pythium was found in all 11 cultivars included in the survey. Occurrence of either Phytophthora or Pythium was unrelated to soil type, planting age, or cultural practices such as bed type, cover crop, mulch, irrigation system, fertilizer application, fungicide use, or the source of plant material used in the fields. Overall, most fields with Phytophthora or Pythium remained largely symptomless under good soil drainage conditions and had similar levels of vigor as those without the pathogens.
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Liu, Bo, Debbie Roos, Shawn Buttler, Brantlee Richter, and Frank J. Louws. "Vegetable Seedling Diseases Associated with Earthworm Castings Contaminated with Phytophthora capsici and Pythium Attrantheridium." Plant Health Progress 13, no. 1 (January 2012): 15. http://dx.doi.org/10.1094/php-2012-0421-01-rs.
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Earthworms and worm castings have been recommended for their beneficial effects in increasing yields and suppressing soilborne diseases. However, in a few cases, earthworm castings have been shown to harbor soilborne pathogens. The research documents that earthworm castings used as an amendment in soilless potting mixes at several organic farms in North Carolina were contaminated with Phytophthora capsici and several Pythium species. Phytophthora capsici and P. attrantheridium were subsequently isolated from rotted roots of vegetable seedlings grown in the potting mix. Commercial producers of earthworm castings should only use clean plant material to maintain earthworms and earthworm castings should be ascertained as pathogen-free before incorporation into plant growth media. Accepted for publication 30 January 2012. Published 21 April 2012.
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Campoverde, E. Vanessa, Georgina Sanahuja, and Aaron J. Palmateer. "A High Incidence of Pythium and Phytophthora Diseases Related to Record-breaking Rainfall in South Florida." HortTechnology 27, no. 1 (February 2017): 78–83. http://dx.doi.org/10.21273/horttech03514-16.
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Florida’s ornamental plant industry flourishes due to environmental conditions that allow for a 12-month growing season. Florida leads the nation in production of tropical foliage, and Miami-Dade County ranks number one in nursery and landscape production with sales reaching $2 billion annually. The well-advertised El Niño pattern made its presence felt this past winter in south Florida with the wettest conditions since record keeping began in 1932. As a result, ornamental nursery growers contended with a higher incidence of root rots, crown rots, and foliar blight diseases, confirmed by samples submitted to the University of Florida’s Extension Plant Diagnostic Clinic in Homestead, FL. The present study focused on environmental conditions occurring over the past 4 years and included rainfall, solar radiation, and temperature variables and examined their influence on the incidence of diseases affecting ornamental plants. Results indicated Pythium and Phytophthora species as the primary plant pathogens responsible for these diseases. The drastic increase of diagnostic samples identified as Pythium and Phytophthora can be attributed to the unusually wet weather experienced. These two oomycetes are well known for causing disease under wet conditions and growers should closely monitor weather forecasts and practice preventative disease management accordingly.
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Pekárová-Kyněrová, B., and M. Kutíková. "Preparation and use of monoclonal antibodies to detect Phytophthora nicotianae var. nicotianae." Plant Protection Science 35, No. 2 (January 1, 1999): 41–46. http://dx.doi.org/10.17221/9673-pps.
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A monoclonal antibody (MAb 18) was prepared against purified mycelial proteins from Phytophthora nicotianae var. nicotianae. The specificity of MAb 18 (lgG class) was tested using indirect ELISA (PTA-ELISA).It cross-reacted with Phytophthora cacto rum, P. cinrzamomi, P. cryptogea, P. fragariae) but not with other fungi (Fusarium oxysporum, Pythium ultimwn and P. oligan drwn) and bacteria (Clavibacter michiganensis subsp. michiganensis) isolated from tomato. Phytophthora nicotianae var. nicotianae was detected in roots and basal stems of artificially infected young tomato plants using indirect ELISA and immunoprinting.
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Caruso, Frank L., Benedict F. Neubauer, and Marc D. Begin. "A histological study of apple roots affected by replant disease." Canadian Journal of Botany 67, no. 3 (March 1, 1989): 742–49. http://dx.doi.org/10.1139/b89-100.
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Little is known about the microscopical symptoms of roots from apple trees suffering from replant disease. Roots were sampled from healthy trees and from such diseased trees in four orchards from May until October. Roots were stained for the detection of mycorrhizal infection and other roots were fixed, dehydrated, embedded in paraffin, sectioned, and stained in safranin and fast green in order to elucidate morphological details. Healthy tree roots possessed considerably higher frequencies of mycorrhizal infection than diseased trees during the entire growing season. Arbuscules and hyphae were very common, vesicles were sometimes present, and possible chlamydospores of Glomus radiatum (Thaxter) Gerd. & Trappe were found in several samples. Whereas roots from healthy trees were structurally intact, roots from declined trees had extensive sloughing away of the epidermal and cortical layers and the cortical cells possessed significant amounts of densely stained material. Nematodes and possible hyphae of Rhizoctonia, Phytophthora, and Pythium were found in roots of declined trees. Althugh the stele of these roots appeared unaltered, hyphae were sometimes observed in the vascular elements.
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Miles, T. D., C. I. Woelk, A. Rojas, and A. M. C. Schilder. "First Report of Pythium sterilum Causing Root Rot of Blueberry in the United States." Plant Disease 95, no. 5 (May 2011): 614. http://dx.doi.org/10.1094/pdis-08-10-0611.
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In September 2009, ~40 declining blueberry plants (Vaccinium corymbosum L. ‘Jersey’) were observed in a poorly drained area of a 30-year-old field near Fennville, MI. The stunted bushes had yellow leaves and defoliation; others were completely dead. The grower reported that the bushes had been declining over several years. Root samples tested positive in a Phytophthora ELISA test (Agdia Inc., Elkhart IN). Twenty root pieces (2 cm long and 2 to 3 mm in diameter) were surface disinfested and plated on Rye A agar; five yielded fungal-like colonies that were subcultured on potato dextrose agar (PDA). One isolate was white and grew slowly (3 to 4 mm/day at 22 to 24°C). Three isolates were white and grew faster (10 to 12 mm/day at 22 to 24°C) in a chrysanthemal pattern. The fifth was a Fusarium sp. DNA of the white colonies was extracted and the internal transcribed spacer (ITS) region was sequenced using ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) primers. The slow-growing morphotype had 99% identity to Phytophthora sp. isolate 92-209C (Accession No. EU106591) in GenBank but failed to induce symptoms in multiple inoculation tests. The fast-growing morphotype (Accession No. HQ398249) had 98% identity to Pythium sterilum UASWS0265 from declining alder stands in Poland (Accession No. DQ525089). Sequencing of the COXII gene using the FM66/FM58 primer set (3) yielded a product (Accession No. HQ721468) with 100% identity to P. sterilum GD32a from forest soil in Poland (Accession No. EF421185). Hyphae were hyaline, coenocytic, and 4 to 7 μm wide with some swellings at the tips (7 to 9 μm wide). No sporangia, oogonia, or antheridia were observed. Mycelium tested positive in the ELISA test described above. According to Agdia Inc., 10 of 19 tested Pythium spp. have shown similar cross reactivity. Pythium spp. are known to cause root rot of blueberries in Oregon (2). In British Columbia, P. sterilum was commonly isolated from roots of declining blueberry bushes (4). P. sterilum Belbahri & Lefort only reproduces asexually (1). Our isolate was similar but did not produce sporangia in water or on PDA, V8 juice agar, Rye A agar, or water agar. Roots of 10 2-month-old ‘Bluecrop’ cuttings were placed in an aqueous suspension of rinsed mycelium (0.1 g/ml) from 21-day-old cultures grown in V8 broth or in sterile deionized water (control). After 1 h, plants were potted in peat moss/perlite (2:1) or autoclaved sand (five each) and placed in a glasshouse at 25°C. After 7 days, inoculated plants in both soil types had wilted or collapsed with significant necrosis on the roots and primary shoot. Control plants showed no symptoms. In a similar experiment with 6-month-old plants in sand, symptoms appeared after 10 to 12 days. The pathogen was recovered from surface-disinfested root and stem sections of all inoculated plants but not control plants and its identity was confirmed by sequencing of the ITS region. To our knowledge, this is the first report of P. sterilum on blueberries in the United States. While this disease appears to be uncommon in Michigan, it is a potential cause of plant decline, the diagnosis of which may be complicated by cross reactivity in ELISA testing. References: (1) L. Belbahri et al. FEMS Microbiol. Lett. 255:209, 2006. (2) D. R. Bryla and R. G. Linderman. HortScience 43:260, 2008. (3) F. N. Martin. Mycologia 92:711, 2000. (4) S. Sabaratnam. BC Plant Health Fund Final Report. B.C. Retrieved from http://www.agf.gov.bc.ca/cropprot/phf_final_report.pdf , 2008.
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Oszako, Tomasz, Katarzyna Sikora, Lassaâd Belbahri, and Justyna A. Nowakowska. "Molecular detection of oomycetes species in water courses." Folia Forestalia Polonica 58, no. 4 (December 1, 2016): 246–51. http://dx.doi.org/10.1515/ffp-2016-0028.
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Abstract In Poland, about 20% of forest nurseries use irrigation water coming from natural superficial reservoirs, presumed to be the first source of infection caused by harmful pathogens belonging to the Oomycota class, especially Phytophthora genus and Pythium genus. The forest nursery is the only place where forest managers can react before pathogens leave it with asymptomatic plants or soil attached to their roots. The aim of this research was detection and identification phytopathogens in water samples. In order to recognise genus Phytophthora or Pythium in water collected from 33 places in five different forest districts in Poland, two DNA-based approaches of identification were applied: (i) the TaqMan probes, and (ii) sequencing of the ITS6/4 region. The genomic DNA was obtained from 17 of 33 investigated water samples. TaqMan probes helped to identify 8 oomycetes present in 17 water samples. Based on ITS rDNA sequencing data, pathogens were identified in 17 cases, and this to the genus level (6 cases) and to the species level (11 cases). In total five Oomycetes species were identified, i.e. 3 Pythium species (Py. citrinum, Py. angustatum, Py. helicoides) and two Phytophthora species (P. lacustris sp. nov. - former taxon Salixsoil, P. gallica sp. nov.).
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Bull, C. T., K. G. Shetty, and K. V. Subbarao. "Interactions Between Myxobacteria, Plant Pathogenic Fungi, and Biocontrol Agents." Plant Disease 86, no. 8 (August 2002): 889–96. http://dx.doi.org/10.1094/pdis.2002.86.8.889.
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Myxobacteria are soil dwelling gram-negative gliding bacteria that form fruiting bodies containing myxospores. Although myxobacteria produce a wide range of antibiotics and lytic enzymes that assist in their ability to prey on other microorganisms, their role in agriculture has received little attention. Myxococcus spp. were isolated from soils in organic and conventionally managed strawberry production and transplant fields in the absence of soil fumigation. Fumigation with methyl bromide and chloropicrin virtually eliminated these organisms from soil. However, soil fumigation had no effect on the frequency of isolation of Myxococcus spp. from strawberry roots. Six Myxococcus spp. were tested in vitro against eight soilborne plant pathogenic fungi (Cylindrocarpon spp., Fusarium oxysporum f. sp. apii, Phytophthora capsici, Pythium ultimum, Rhizoctonia spp., Sclerotinia minor, Verticillium albo-atrum, and V. dahliae) and against two fungal biological control agents (Gliocladium virens and Trichoderma viride). Phytophthora capsici, Pythium ultimum, Rhizoctonia spp., S. minor, and T. viride were completely inhibited by all of the Myxococcus spp. tested. F. oxysporum f. sp. apii was the least sensitive to the myxobacteria, and no inhibition occurred with some Myxococcus spp. Inhibition of the other fungi tested was variable. Myxococcus coralloides inhibited nearly all the fungi tested. The ability of bacterial biological control agents to produce antibiotics and other secondary metabolites determined whether or not they were lysed by myxobacteria. Secondary metabolite production regulated by gacS protected Pseudomonas fluorescens strain CHA0 from lysis by myxobacteria. More specifically, phenazine antibiotics produced by Pseudomonas aureofaciens strain 30–84 protected it from lysis.
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Watanabe, Hideki, Yoshihiro Taguchi, Mitsuro Hyakumachi, and Koji Kageyama. "Pythium and Phytophthora species associated with root and stem rots of kalanchoe." Journal of General Plant Pathology 73, no. 2 (April 10, 2007): 81–88. http://dx.doi.org/10.1007/s10327-006-0338-0.
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Zinati, Gladis M. "Compost in the 20th Century: A Tool to Control Plant Diseases in Nursery and Vegetable Crops." HortTechnology 15, no. 1 (January 2005): 61–66. http://dx.doi.org/10.21273/horttech.15.1.0061.
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The discovery of disease suppression in certain bark composts increased the interest in using compost as growing substrate to control root rot diseases caused by Phytophthora cinnamomi. Disease suppression mechanisms include antibiosis, competition, hyperparasitism, and induced systemic resistance. Although abiotic factors may influence disease suppression, the latter is often based on microbial interactions—the two common mechanisms being general for pythium (Pythium spp.) and phytophthora root rot (Phytophthora spp.) and specific for rhizoctonia (Rhizoctonia solani). The discovery of disease suppression agents in compost led to the development of biocontrol agent-fortified compost during the last decade of the 20th century. The suggested recommendations for future research and extension outreach may include 1) development of methods to manage bacterial and viral diseases through the use of compost; 2) exploration of the potential effects of fortified compost on insect pests suppression; 3) improvement of inoculation methods of composts with biocontrol agents to produce consistent levels of disease suppression at the commercial scale; 4) development of effective fortified compost teas for suppressing foliar diseases; 5) education of compost producers on methods of production of fortified compost that suppress specific diseases; and 6) education of end-users on uses of fortified compost and its by-products.
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Bryla, David R., and Robert G. Linderman. "Implications of Irrigation Method and Amount of Water Application on Phytophthora and Pythium Infection and Severity of Root Rot in Highbush Blueberry." HortScience 42, no. 6 (October 2007): 1463–67. http://dx.doi.org/10.21273/hortsci.42.6.1463.
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A 2-year study was done in Oregon to determine the effects of irrigation method and level of water application on the development of root rot in northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). Plants were grown on mulched, raised beds and irrigated by overhead sprinklers, microsprays, or drip at 50%, 100%, and 150% of the estimated crop evapotranspiration requirement. Soil at the site was a silty clay loam. By the end of the first season, plants were largest with drip, intermediate-sized with microsprays and smallest with sprinklers; however, this was not the case the next season. By the end of year 2, plants irrigated by drip had less canopy cover, fewer new canes, lower pruning weights, and only half the shoot and root dry weight as plants irrigated by sprinklers or microsprays. Destructive sampling revealed that the field was infested by root rot. Less growth with drip was association with higher levels of infection by the root pathogen, Phytophthora cinnamomi. Phytophthora infection increased with water application, regardless of irrigation method, but averaged 14% with drip and only 7% with sprinklers and microsprays. Roots were also infected by Pythium spp. Pythium infection likewise increased with the total amount of water applied but, unlike P. cinnamomi, was similar among irrigation methods. Overall, drip irrigation maintained higher soil water content near the base of the plants than sprinklers and microsprays, resulting in conditions more favorable to root rot. Sprinklers and microsprays may be better alternatives than drip at sites prone to problems with the disease.
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Zahid, M. I., G. M. Gurr, A. Nikandrow, M. Hodda, W. J. Fulkerson, and H. I. Nicol. "Survey of fungi and nematodes associated with root and stolon diseases of white clover in the subtropical dairy region of Australia." Australian Journal of Experimental Agriculture 41, no. 8 (2001): 1133. http://dx.doi.org/10.1071/ea01015.
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A survey of 12 white clover-based dairy pastures on the north coast of New South Wales and south-eastern Queensland, Australia, detected 65 species of fungi and 6 nematode species. The fungi included species of Fusarium, Gliocladium, Codinaea, Alternaria, Colletotrichum, Drechslera, Rhizoctonia, Phoma, Pythium, Phytophthora, Penicillium, Rhizopus and Trichoderma from roots and stolons of white clover. Fungal rots of roots and stolons were most severe during the summer months (November and January samples), while root-knot symptoms caused by plant parasitic nematodes were more severe in June. Sedentary endoparasitic nematodes Meloidogyne trifoliophila, Heterodera trifolii and the ectoparasitic nematode Helicotylenchus dihystera were the numerically dominant nematodes in the region. Other nematode species, including Pratylenchus, Xiphinema and Tylenchorhynchus, were present at lower frequencies and principal component analysis indicated that these were less important as white clover pathogens. Meloidogyne trifoliophila was detected for the first time in Australia and was present at all sites. Many of the fungi and nematodes found are common pathogens of white clover. These pathogens are likely to be contributing to the poor seedling performance, growth and persistence of white clover typical in dairy pastures of the subtropical east coast of Australia.
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Mohamed, N., J. Lherminier, M. J. Farmer, J. Fromentin, N. Béno, V. Houot, M. L. Milat, and J. P. Blein. "Defense Responses in Grapevine Leaves Against Botrytis cinerea Induced by Application of a Pythium oligandrum Strain or Its Elicitin, Oligandrin, to Roots." Phytopathology® 97, no. 5 (May 2007): 611–20. http://dx.doi.org/10.1094/phyto-97-5-0611.
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Pythium oligandrum is known to display antagonistic activities against several species of pathogenic fungi. It also produces an elicitor of plant defense named oligandrin, which belongs to the elicitin family (10-kDa proteins synthesized by Phytophthora and Pythium species). Here, the potential of P. oligandrum or its purified elicitin to limit the progression of B. cinerea on grapevine leaf and the resulting plant-microorganism interactions are described. P. oligandrum or oligandrin were applied to roots, and changes in the ultrastructure and at the molecular level were examined. When B. cinerea was applied to leaves of pretreated plants, leaf invasion was limited and the protection level reached about 75%. On leaf tissues surrounding B. cinerea inoculation, modifications of cuticle thickness, accumulation of phenolic compounds, and cell wall apposition were observed, indicating that grapevine can be considered reactive to elicitins. No macroscopic hypersensitive reaction associated with the elicitation treatment was observed. At the molecular level, the expression of three defense-related genes (LTP-1, β-1,3-glucanase, and stilbene synthase) was studied. RNAs isolated from B. cinerea-infected leaves of grapevine challenged or not with P. oligandrum or oligandrin were analyzed by real-time reverse transcription-polymerase chain reaction. In grapevine leaves, LTP-1 gene expression was enhanced in response to oligandrin, and RNA transcript levels of β-1,3-glucanase and stilbene synthase increased in response to all treatments with different magnitude. Taken together, these results open new discussion on the concept of plant reactivity to elicitins, which has until now, been mainly based on plant hypersensitive responses.
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Weiland, Jerry E., Carolyn F. Scagel, Niklaus J. Grünwald, E. Anne Davis, Bryan R. Beck, and Val J. Fieland. "Variation in Disease Severity Caused by Phytophthora cinnamomi, P. plurivora, and Pythium cryptoirregulare on Two Rhododendron Cultivars." Plant Disease 102, no. 12 (December 2018): 2560–70. http://dx.doi.org/10.1094/pdis-04-18-0666-re.
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Rhododendrons are an important crop in the ornamental nursery industry, but are prone to Phytophthora root rot. Phytophthora root rot is a continuing issue on rhododendrons despite decades of research. Several Phytophthora species are known to cause root rot, but most research has focused on P. cinnamomi, and comparative information on pathogenicity is limited for other commonly encountered oomycetes, including Phytophthora plurivora and Pythium cryptoirregulare. In this study, three isolates each of P. cinnamomi, P. plurivora, and Py. cryptoirregulare were used to inoculate rhododendron cultivars Cunningham’s White and Yaku Princess at two different inoculum levels. All three species caused disease, especially at the higher inoculum level. P. cinnamomi and P. plurivora were the most aggressive pathogens, causing severe root rot, whereas Py. cryptoirregulare was a weak pathogen that only caused mild disease. Within each pathogen species, isolate had no influence on disease. Both P. cinnamomi and P. plurivora caused more severe disease on Cunningham’s White than on Yaku Princess, suggesting that the relative resistance and susceptibility among rhododendron cultivars might be similar for both pathogens. Reisolation of P. cinnamomi and P. plurivora was also greater from plants exhibiting aboveground symptoms of wilting and plant death and belowground symptoms of root rot than from those without symptoms. Results show that both P. cinnamomi and P. plurivora, but not Py. cryptoirregulare, are important pathogens causing severe root rot in rhododendron. This study establishes the risks for disease resulting from low and high levels of inoculum for each pathogen. Further research is needed to evaluate longer term risks associated with low inoculum levels on rhododendron health and to explore whether differences among pathogen species affect disease control.
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Toppe, B., E. Aanonsen, and S. Klemsdal. "First Report of Root Rot and Stem Blight Caused by Phytophthora palmivora in Eustoma grandiflorum." Plant Disease 88, no. 2 (February 2004): 224. http://dx.doi.org/10.1094/pdis.2004.88.2.224b.
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Eustoma grandiflorum (Raf.) Shinn., commonly referred to as Lisianthus or Texas bluebell, is grown on a limited but increasing scale in Norwegian greenhouses. In autumn 1999, E. grandiflorum plants with brown rotten roots and wilting foliage were collected from a cut-flower production facility in southeastern Norway. Symptoms were difficult to distinguish from those caused by Pythium spp. or early attack of Fusarium spp. For diagnosis, root and stem segments surface sterilized by dipping in alcohol and hypochlorite were plated on potato dextrose agar. Phytophthora sp. was isolated consistently from diseased roots and stems. Suspected Phytophthora sp. isolates were transferred to selective agar medium containing hymexazol and identified by morphological characteristics and DNA sequence homology (1). The fungus was characterized by stellate mycelium, lack of oogonia in single culture, sympodial sporangiophores, and production of numerous papillate, ellipsoid sporangia that were caduceus with small pedicels in water. Optimum temperature for mycelium growth was 25 to 30°C, with limited growth at 10 and 35°C. The DNA sequence of the polymerase chain reaction amplified internal transcribed spacer (ITS1 and ITS2) regions of rDNA, confirmed the identification as P. palmivora. Pathogenicity studies were conducted by inoculating nine, 12-week-old E. grandiflorum plants grown in 10-cm pots with peat substrate at 24°C with artificial light (120 W/m2) for 10 h per day, with a zoospore suspension or an agar piece toward the plant stem. The pathogenicity study was repeated once. In both experiments, all plants except uninoculated controls, died within 3 weeks after inoculation. P. palmivora was reisolated from diseased plants. In later greenhouse experiments, more than 50% of plants showed disease symptoms when adding 1,000 zoospores of P. palmivora per pot. ‘Ecco Yellow’ was more susceptible than ‘Flamenco Purple’. The pathogen was as aggressive as Fusarium avenaceum in pathogenicity studies. Since E. grandiflorum is grown on a limited scale in Norway, we lack experience with the economic impact of this disease in the cut-flower industry. To our knowledge, this is the first report of P. palmivora in E. grandiflorum. Reference: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.
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Benavent-Celma, Clara, Alexandra Puertolas, Debbie McLaggan, Pieter van West, and Steve Woodward. "Pathogenicity and Host Range of Pythium kashmirense—A Soil-Borne Oomycete Recently Discovered in the UK." Journal of Fungi 7, no. 6 (June 12, 2021): 479. http://dx.doi.org/10.3390/jof7060479.
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During a survey of oomycetes in ornamental plants carried out at the University of Aberdeen in 2014–2015, Pythium kashmirense was isolated from a specimen of Viburnum plicatum ‘Lanarth’, the first report of this oomycete in the UK (and in Europe). Pathogenicity of a Py. kashmirense isolate was examined using a range of plant species. Inoculations were carried out under controlled conditions in the absence of other Pythium and Phytophthora species, on Glycine max (soya bean), Phaseolus vulgaris (common bean), Lupinus angustifolius (blue lupin), Cucumis sativa (cucumber) and Viburnum opulus. The majority of inoculations caused pre-emergence damping-off, as well as seed rot and root rot. In the in vitro assays, germination rates (%) of soya bean and blue lupin seeds were less than 50%; in the in vivo inoculations on plants, over 50% of soya bean, blue lupin and common bean plants died; in contrast, cucumber plants showed lower susceptibility in pathogenicity tests, with an approximately 80% germination rate in in vitro tests, and 25% dead plants in the in planta inoculations. Inoculations carried out on root systems of Viburnum opulus caused severe necrosis and root rot. Little research was previously conducted on pathogenicity of Py. kashmirense and its relationship with losses in crop yield and quality. The present study showed varying virulence on the different plant species tested after inoculation with Py. kashmirense. Despite the lack of clear host specialization, infection by Py. kashmirense decreased seedling survival and health of plants in a range of important agricultural and ornamental plant species.
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Radmer, L., G. Anderson, D. M. Malvick, J. E. Kurle, A. Rendahl, and A. Mallik. "Pythium, Phytophthora, and Phytopythium spp. Associated with Soybean in Minnesota, Their Relative Aggressiveness on Soybean and Corn, and Their Sensitivity to Seed Treatment Fungicides." Plant Disease 101, no. 1 (January 2017): 62–72. http://dx.doi.org/10.1094/pdis-02-16-0196-re.
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Pythium spp. cause seed decay, damping-off, and root rot in soybean and corn; however, their diversity and importance as pathogens in Minnesota are unknown. Our objectives were to identify the Pythium spp. present in Minnesota soybean fields, determine their aggressiveness on corn and soybean, and investigate their sensitivity to seed treatment fungicides. For identification, sequences obtained using internal transcribed space ITS4 and ITS1 primers were compared with reference sequences in the National Center for Biotechnology Information database. Seedling and soil samples yielded over 30 oomycete species. Aggressiveness was determined using two methods; a seed assay, which also examined temperature effects on aggressiveness, and a seedling assay. Of 21 species evaluated, seven Pythium spp. were pathogenic on both soybean and corn, reducing root growth by 20% or more while two Pythium and one Phytopythium spp. were pathogenic only on soybean. Aggressiveness of many isolates increased as temperature increased from 15°C to 25°C. The sensitivity of 10 pathogenic species to azoxystrobin, ethaboxam, mefenoxam, pyraclostrobin, or trifloxystrobin was tested. EC50 values for mefenoxam and ethaboxam were 10−2 of those to strobilurin fungicides. Pythium spp. in Minnesota are diverse and a significant cause of seedling disease on soybean and corn. Most Pythium spp. isolated in this study were more sensitive to mefenoxam and ethaboxam than to strobilurin fungicides.
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Samac, Deborah A., Samuel Schraber, and Stuart Barclay. "A Mineral Seed Coating for Control of Seedling Diseases of Alfalfa Suitable for Organic Production Systems." Plant Disease 99, no. 5 (May 2015): 614–20. http://dx.doi.org/10.1094/pdis-03-14-0240-re.
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Most alfalfa seed is treated with the fungicide mefenoxam (Apron XL) for control of soilborne seedling diseases caused by Phytophthora medicaginis and Pythium spp. However, Apron XL is not active against Aphanomyces euteiches, the causal agent of Aphanomyces root rot (ARR), an important component of the alfalfa seedling root rot complex. Moreover, Apron XL-treated seed cannot be used in organic production systems. A seed coating using aluminosilicate (natural zeolite) at a rate of 0.33 g of zeolite per gram of alfalfa seed was tested as an alfalfa seed treatment. Inoculated growth chamber trials were conducted to determine the percentage of seedlings protected from Phytophthora root rot (PRR) and ARR. The mineral seed coating resulted in significantly greater control of PRR, with a mean of 89% healthy seedlings (disease score of 1 or 2 on a 1-to-5 scale) compared with the Apron XL treatment, with a mean of 38% healthy seedlings, or the control treatment, with 15% healthy seedlings. The mineral seed coating also resulted in significantly greater protection against ARR, with 67% healthy seedlings compared with 3 and 2% healthy seedlings with the Apron XL and control treatments, respectively. The coated seed were used for in vitro assays with Pythium ultimum and P. paroecandrum to test for protection from seed rot and damping off. The mineral seed coating resulted in a significantly greater percentage of healthy seedlings compared with the Apron XL and control treatments. In growth chamber assays with naturally infested field soils with a range of disease pressure, the mineral seed coating resulted in a similar or greater percentage of healthy plants than the Apron XL treatment. The mineral coating had no effect on in vitro growth of Sinorhizobium meliloti, and nodule numbers were similar on roots from mineral-coated and untreated seed. These experiments indicate that the zeolite seed coating is a promising means of controlling seedling diseases in alfalfa production systems.
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Labuschagne, N., A. H. Thompson, and W. J. Botha. "First Report of Stem and Root Rot of Tomato Caused by Phytophthora capsici in South Africa." Plant Disease 87, no. 12 (December 2003): 1540. http://dx.doi.org/10.1094/pdis.2003.87.12.1540a.
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Tomato plants, grown in open hydroponic systems under shadecloth and plastic near Barberton and Pretoria in South Africa and Srelebi Phikwe in Botswana, developed symptoms of wilting with brown-to-black cankers on the lower stems, blackening of the vascular tissues, and root rot. Pathogens isolated from affected tissues were identified as Phytophthora capsici Leonian (1) and Pythium aphanidermatum (Edson) Fitzp. (2).They occurred separately or together. Pythium aphanidermatum has previously been recorded on tomato in South Africa. P. capsici isolates were papillate, caducous, grew at >36°C, had tapered sporangial bases, and a maximum sporangial length of >70 μm. Koch's postulates were confirmed by inoculating 4-week-old tomato seedlings (cv. Floradade) grown at 22 to 30°C in a steam-pasteurized mixture of sawdust compost, pine bark, and vermiculite (3:2:1). Plugs from V8 juice agar cultures of P. capsici were placed on wounds made on the stems of 10 seedlings. Ten wounded uninoculated plants served as controls. Water-soaked lesions were visible on the stems of all inoculated plants after 2 days. Control plants remained healthy. After 4 days, lesions turned dark brown with affected plants wilted or dead. Reisolation yielded P. capsici. The experiment was repeated with similar results. To our knowledge, this is the first report of P. capsici on tomatoes in South Africa. References: (1) A. H. Thompson et al. S. Afr. J. Bot. 60:257, 1994.(2) W. Dick. Keys to Pythium. University of Reading Press, Reading, U.K., 1990.
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Rojas, J. Alejandro, Timothy D. Miles, Michael D. Coffey, Frank N. Martin, and Martin I. Chilvers. "Development and Application of qPCR and RPA Genus- and Species-Specific Detection of Phytophthora sojae and P. sansomeana Root Rot Pathogens of Soybean." Plant Disease 101, no. 7 (July 2017): 1171–81. http://dx.doi.org/10.1094/pdis-09-16-1225-re.
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Phytophthora root rot of soybean, caused by Phytophthora sojae, is one of the most important diseases in the Midwestern United States, and is estimated to cause losses of up to 1.2 million metric tons per year. Disease may also be caused by P. sansomeana; however, the prevalence and damage caused by this species is not well known, partly due to limitations of current diagnostic tools. Efficient, accurate, and sensitive detection of pathogens is crucial for management. Thus, multiplex qPCR and isothermal RPA (recombinase polymerase amplification) assays were developed using a hierarchical approach to detect these Phytophthora spp. The assays consist of a genus-specific probe and two species-specific probes that target the atp9-nad9 region of the mitochondrial genome that is highly specific for the genus Phytophthora. The qPCR approach multiplexes the three probes and a plant internal control. The RPA assays run each probe independently with a plant internal control multiplexed in one amplification, obtaining a result in as little as 20 mins. The multicopy mitochondrial genome provides sensitivity with sufficient variability to discern among different Phytophthora spp. The assays were highly specific when tested against a panel of 100 Phytophthora taxa and range of Pythium spp. The consistent detection level of the assay was 100 fg for the qPCR assay and 10 pg for the RPA assay. The assays were validated on symptomatic plants collected from Michigan (U.S.) and Ontario (Canada) during the 2013 field season, showing correlation with isolation. In 2014, the assays were validated with samples from nine soybean producing states in the U.S. The assays are valuable diagnostic tools for detection of Phytophthora spp. affecting soybean.
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Ivors, Kelly L., Z. Gloria Abad, and D. Michael Benson. "Evaluating the Pathogenicity of Pythium vexans Isolates from Fraser Fir in North Carolina." Plant Health Progress 9, no. 1 (January 2008): 8. http://dx.doi.org/10.1094/php-2008-1006-01-rs.
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The pathogenicity of Pythium vexans isolates collected from fir samples with typical root rot symptoms in North Carolina was evaluated on Fraser fir seedlings (Abies fraseri). Two replicated pathogenicity trials involving seven treatments were conducted in the lath house and greenhouse. Although the P. vexans isolates examined in these trials were able to colonize Fraser fir root systems, they did not cause mortality or incite root rot symptoms. In comparison, Phytophthora cinnamomi, a known aggressive pathogen of Fraser fir, caused severe root rot symptoms in all plants. These experiments provided no evidence that P. vexans is a pathogen of Fraser fir. Accepted for publication 12 July 2008. Published 6 October 2008.
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Derviş, Sibel, Şahimerdan Türkölmez, Osman Çiftçi, Göksel Özer, Çiğdem Ulubaş Serçe, and Murat Dikilitas. "Phytopythium litorale: A Novel Killer Pathogen of Plane (Platanus orientalis) Causing Canker Stain and Root and Collar Rot." Plant Disease 104, no. 10 (October 2020): 2642–48. http://dx.doi.org/10.1094/pdis-01-20-0141-re.
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Decline symptoms associated with lethal stem and branch canker stain along with root and collar rots were observed on 5- to 7-year-old roadside oriental plane trees (Platanus orientalis) in Diyarbakır, Turkey. Above-ground symptoms included leaf necrosis, leaf curling, extensive bluish or blackish staining of shoots, branches, stem bark, and wood surfaces, as well as stem cankers and exfoliation of branch bark scales. A general decline of the trees was distinctly visible from a distance. A Phytophthora/Pythium-like oomycete species with globose to ovoid, often papillate and internally proliferating sporangia was consistently isolated from the fine and coarse roots and stained branch parts and shoots. The pathogen was identified as Phytopythium litorale based on several morphological features. Partial DNA sequences of three loci, including nuclear rDNA internal transcribed spacer (ITS) and the large ribosomal subunit (LSU), and mitochondrial cytochrome c oxidase subunit II (coxII) confirmed the morphological identification. All P. litorale isolates were homothallic, developing gametangia, ornamented oogonia with elongate to lobate antheridia. Pathogenicity of P. litorale was tested by inoculation on excised shoots and by root inoculation on seedlings. P. litorale produced large lesions and blights on shoots in just 5 days and killed 100% of the seedlings in a month. This paper presents the first confirmed report of P. litorale as an important pathogen on a plant species causing branch and stem cankers, and root and collar rot, in and on P. orientalis, resulting in a rapid decline of trees and suggesting a threat to plane.
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Sealy, Ramsey, and Michael R. Evans. "EFFICACY OF BIOLOGICAL AMENDMENTS ON POSTTRANSPLANT ROOT ROT." HortScience 40, no. 3 (June 2005): 880b—880. http://dx.doi.org/10.21273/hortsci.40.3.880b.
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Biological substrate amendments including SG-11, Subtilex, SoilGuard, ActinoIron, Companion, RootShield and BioYield were evaluated for their efficacy to control common soil-borne fungal and fungal-like pathogens when incorporated into the substrate at transplanting. The biological agents were incorporated into an 80% Sphagnum peat and 20% perlite substrate at the label recommended rates and four-to-six-leaf plugs of the test species were transplanted into the substrates. Substrates were either inoculated or uninoculated with a test pathogen. Pathogen-host combinations included Pythium ultimum on geranium (Pelargonium ×hortorum), Phytophthora nicotianae and Pythium aphanidermatum on vinca (Catharanthus roseus), and Theilaviopsis basicoli on pansy (Viola ×wittrockiana). The incidence of disease development, plant mortality and root fresh weights did not differ among the biological agents and the inoculated controls. Therefore, under the conditions of this study, the biological agents did not provide significant disease suppression. Pansy and vinca plants grown in uninoculated substrates amended with Subtilex had significantly higher shoot dry weights than those grown in unamended substrates. Pansy, vinca and tomato plants grown in uninoculated substrates amended with SG-11 had significantly higher shoot dry weights than those grown in unamended substrates.
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Zachow, Christin, Ghazaleh Jahanshah, Irene de Bruijn, Chunxu Song, Federica Ianni, Zoltán Pataj, Heike Gerhardt, et al. "The Novel Lipopeptide Poaeamide of the Endophyte Pseudomonas poae RE*1-1-14 Is Involved in Pathogen Suppression and Root Colonization." Molecular Plant-Microbe Interactions® 28, no. 7 (July 2015): 800–810. http://dx.doi.org/10.1094/mpmi-12-14-0406-r.
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Endophytic Pseudomonas poae strain RE*1-1-14 was originally isolated from internal root tissue of sugar beet plants and shown to suppress growth of the fungal pathogen Rhizoctonia solani both in vitro and in the field. To identify genes involved in its biocontrol activity, RE*1-1-14 random mutagenesis and sequencing led to the identification of a nonribosomal peptide synthetase (NRPS) gene cluster predicted to encode a lipopeptide (LP) with a 10-amino-acid peptide moiety. The two unlinked gene clusters consisted of three NRPS genes, designated poaA (cluster 1) and poaB and poaC (cluster 2), spanning approximately 33.7 kb. In silico analysis followed by chemical analyses revealed that the encoded LP, designated poaeamide, is a structurally new member of the orfamide family. Poaeamide inhibited mycelial growth of R. solani and different oomycetes, including Phytophthora capsici, P. infestans, and Pythium ultimum. The novel LP was shown to be essential for swarming motility of strain RE*1-1-14 and had an impact on root colonization of sugar beet seedlings The poaeamide-deficient mutant colonized the rhizosphere and upper plant cortex at higher densities and with more scattered colonization patterns than the wild type. Collectively, these results indicate that Pseudomonas poae RE*1-1-14 produces a structurally new LP that is relevant for its antagonistic activity against soilborne plant pathogens and for colonization of sugar beet roots.
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Mazzola, Mark. "Elucidation of the Microbial Complex Having a Causal Role in the Development of Apple Replant Disease in Washington." Phytopathology® 88, no. 9 (September 1998): 930–38. http://dx.doi.org/10.1094/phyto.1998.88.9.930.
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Systematic studies were conducted to elucidate the role of different soil microbial groups in the development of apple replant disease. Populations of targeted microorganisms were reduced by the application of semiselective biocides and soil pasteurization. Bacteria were not implicated in the disease, because application of the antibiotic chloramphenicol reduced soil populations of bacteria but failed to improve growth of apple transplants, while enhanced growth was achieved at pasteurization temperatures that did not alter attributes of the bacterial community recovered from apple roots. Populations of Pratylenchus penetrans were below the damage threshold level in eight of nine orchards surveyed, and nematicide applications failed to enhance apple growth in four of five replant soils tested, indicating that plant parasitic nematodes have a minor role or no role in disease development. Application of the fungicide difenconazole or metalaxyl enhanced growth of apple in all five replant soils, as did fludioxinil in the two soils tested. Soil pasteurization enhanced growth of apple and resulted in specific changes in the composition of the fungal community isolated from the roots of apple seedlings grown in these treated soils. Cylindrocarpon destructans, Phytophthora cactorum, Pythium spp., and Rhizoctonia solani were consistently isolated from symptomatic trees in the field and were pathogenic to apple. However, the composition of the Pythium and Rhizoctonia component and the relative contribution of any one component of this fungal complex to disease development varied among the study orchards. These findings clearly demonstrate that fungi are the dominant causal agents of apple replant disease in Washington state.
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Vita, P. De, M. S. Serrano, C. Ramo, C. Aponte, L. V. García, L. Belbahri, and M. E. Sánchez. "First Report of Root Rot Caused by Pythium spiculum Affecting Cork Oaks at Doñana Biological Reserve in Spain." Plant Disease 97, no. 7 (July 2013): 991. http://dx.doi.org/10.1094/pdis-10-12-0952-pdn.
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Cork oaks (Quercus suber L.) are key tree species at Doñana Biological Reserve (DBR), Huelva, Spain. Sampling was conducted on a total of 13 trees exhibiting symptoms of decline (foliar wilting and defoliation, branch dieback, and root necrosis). In 2008. Phytophthora cinnamomi was isolated from feeder roots of one tree and Pythium spiculum from two additional oaks. In 2011, both pathogens were isolated from six oaks, only P. cinnamomi from three oaks, and only Py. spiculum from one oak. This expansion was associated with high winter rainfall levels since 2009 that led to long periods of soil flooding. While P. cinnamomi is well known to cause a root disease on Q. suber (2), P. spiculum is a newly described species isolated from Quercus, Vitis, Prunus, Castanea, and Celtis species, but its pathogenicity was demonstrated only on Q. ilex (syn. Q. rotundifolia) (1). Pathogenicity tests were conducted on 4-year-old Q. suber plants. Inocula consisted of two isolates of Py. spiculum from DBR (DO8 and DO36 from Q. suber). For comparison with these, three isolates previously tested on Q. ilex (1) were included: two isolates of Py. spiculum, PA54 (from Q. suber) and PE156 (from Q. ilex); and one isolate of P. cinnamomi, PE90 (from Q. ilex). All these isolates came from the Andalucía region, stored at the oomycete collection of the University of Córdoba, and showed a 99 to 100% homology with their expected ITS sequences in GenBank (DQ196131 for Py. spiculum and AY943301 for P. cinnamomi). Inoculum was prepared by shaking and mixing propagule-bearing mycelium produced in carrot broth petri dishes (20°C, 4 weeks) in sterile water, to produce a concentration of 3 × 104 oospores × ml−1 (Py. spiculum) or 3 × 104 chlamydospores × ml−1 (P. cinnamomi). One hundred milliliters of inoculum was applied to each root (1). There were 10 inoculated plants per isolate and 10 non-inoculated control plants. All plants were waterlogged 2 days per week to favor root infection and maintained in an acclimatised greenhouse (12–28°C). Three months later, the inoculated plants showed symptoms of root necrosis that resulted in foliar wilting followed occasionally by defoliation. Control plants did not develop foliar symptoms nor root necrosis. Root damage severity assessed on a 0 to 4 scale (3) exhibited significant differences (P < 0.05) in relation to the control plants for all the isolates tested, with isolate PE90 (P. cinnamomi) and isolates PA54, DO8, and DO36 (P. spiculum) all averaging a root necrosis value of 2.5. Isolate PE156 of P. spiculum produced values of root necrosis (1.6 in average) significantly lower (P < 0.05) than the rest. This isolate belongs to the low virulence group of P. spiculum described on Q. ilex (1). The inoculated oomycete was always reisolated from necrotic roots and never from roots of control plants. To the best of our knowledge, this is the first report of P. spiculum as the cause of root rot of Q. suber. References: (1) Romero et al. J. Phytopathol. 155:289, 2007. (2) Sánchez et al. For. Pathol. 32:5, 2002. (3) Sánchez et al. For. Pathol. 35:115, 2005.
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Pinkerton, J. N., K. L. Ivors, P. W. Reeser, P. R. Bristow, and G. E. Windom. "The Use of Soil Solarization for the Management of Soilborne Plant Pathogens in Strawberry and Red Raspberry Production." Plant Disease 86, no. 6 (June 2002): 645–51. http://dx.doi.org/10.1094/pdis.2002.86.6.645.
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Root rot caused by Phytophthora fragariae var. fragariae and P. fragariae var. rubi are major concerns in strawberry and raspberry production in the Pacific Northwest. Of lesser importance is black root rot of strawberry, caused by a complex of fungi and nematodes. Soil solarization was evaluated in 1997 in a strawberry planting and in 1998 in a raspberry planting for: (i) enhancing plant health and growth, and (ii) reducing population densities of root-destroying pathogens. Plots were solarized from mid-July to mid-September. Maximum and mean soil temperatures in solarized plots recorded at 10 cm depth were 48 and 33°C in the strawberry plots and 46 and 29°C in the raspberry plots. These temperatures were 7 to 17°C higher than temperatures recorded in nonsolarized plots. Soil collected after solarization was assayed by growing bait plants, cv. Totem strawberry or cv. Qualicum raspberry, at 15°C for 6 weeks in saturated soil to promote infections. Root health and plant growth were evaluated after 6 weeks. Solarization significantly reduced (P < 0.05) root necrosis and increased root weight of bait plants compared to plants grown in soil from nonsolarized plots. Infection of strawberry roots by P. fragariae, Pythium, Rhizoctonia, and Cylindrocarpon spp. was reduced (P < 0.05) by solarization in sampled soil. Disease was reduced in cv. Hood strawberries and Qualicum and Skeena red raspberries planted in solarized field plots. In the second growing season, total number and number of healthy primocanes of Qualicum plants were greater (P < 0.05) in solarized plots compared to nonsolarized plots. Solarization combined with applications of mefenoxam was no more effective in controlling diseases than solarization alone, but better than mefenoxam alone. Skeena plants responded similarly, but the differences were not significant. Red raspberry plants growing in solarized soil yielded more fruit than plants growing in nonsolarized soil in the third year after solarization. Solarization has potential as a component in an integrated pest management program of root diseases in raspberry and strawberry production, particularly within the first 2 years following planting.
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Guajardo, Jeannette, Sebastián Saa, Natalia Riquelme, Gregory Browne, Cristian Youlton, Mónica Castro, and Ximena Besoain. "Characterization of Oomycete Species Associated With Root and Crown Rot of English Walnut in Chile." Plant Disease 103, no. 4 (April 2019): 691–96. http://dx.doi.org/10.1094/pdis-07-18-1160-re.
Full textAbstract:
English (Persian) walnut (Juglans regia) trees affected by root and crown rot were surveyed in five regions of central Chile between 2015 and 2017. In each region, nine orchards, ranging from 1 to 21 years old, were randomly selected and inspected for incidence and severity of tree decline associated with crown and root rot. Soil and symptomatic crown and root tissues were collected and cultured in P5ARP semiselective medium to isolate potential oomycete pathogens, which were identified through morphology and molecularly using ITS sequences in the rDNA gene and beta tubulin gene. The most frequently isolated species was Phytophthora cinnamomi. Pathogenicity tests were conducted with representative oomycete isolates. P. cinnamomi, P. citrophthora, and Pythium ultimum were all pathogenic in J. regia. Nevertheless, only P. cinnamomi and P. citrophthora were pathogenic to English walnut. Py. ultimum caused limited levels of root damage to English walnut seedlings. Our research indicates that as the Chilean walnut industry has expanded, so have walnut crown and root rots induced by oomycetes.
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Picard, Karine, Yves Tirilly, and Nicole Benhamou. "Cytological Effects of Cellulases in the Parasitism of Phytophthora parasitica by Pythium oligandrum." Applied and Environmental Microbiology 66, no. 10 (October 1, 2000): 4305–14. http://dx.doi.org/10.1128/aem.66.10.4305-4314.2000.
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ABSTRACT The ubiquitous oomycete Pythium oligandrum is a potential biocontrol agent for use against a wide range of pathogenic fungi and an inducer of plant disease resistance. The ability ofP. oligandrum to compete with root pathogens for saprophytic colonization of substrates may be critical for pathogen increase in soil, but other mechanisms, including antibiosis and enzyme production, also may play a role in the antagonistic process. We used transmission electron microscopy and gold cytochemistry to analyze the intercellular interaction between P. oligandrum andPhytophthora parasitica. Growth of P. oligandrum towards Phytophthora cells correlated with changes in the host, including retraction of the plasma membrane and cytoplasmic disorganization. These changes were associated with the deposition onto the inner host cell surface of a cellulose-enriched material. P. oligandrum hyphae could penetrate the thickened host cell wall and the cellulose-enriched material, suggesting that large amounts of cellulolytic enzymes were produced. Labeling of cellulose with gold-complexed exoglucanase showed that the integrity of the cellulose was greatly affected both along the channel of fungal penetration and also at a distance from it. We measured cellulolytic activity of P. oligandrum in substrate-free liquid medium. The enzymes present were almost as effective as those from Trichoderma viride in degrading both carboxymethyl cellulose and Phytophthora wall-bound cellulose. P. oligandrum and its cellulolytic enzymes may be useful for biological control of oomycete pathogens, includingPhytophthora and Pythium spp., which are frequently encountered in field and greenhouse production.
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Mazzola, Mark. "Transformation of Soil Microbial Community Structure and Rhizoctonia-Suppressive Potential in Response to Apple Roots." Phytopathology® 89, no. 10 (October 1999): 920–27. http://dx.doi.org/10.1094/phyto.1999.89.10.920.
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Changes in the composition of soil microbial communities and relative disease-suppressive ability of resident microflora in response to apple cultivation were assessed in orchard soils from a site possessing trees established for 1 to 5 years. The fungal community from roots of apple seedlings grown in noncultivated orchard soil was dominated by isolates from genera commonly considered saprophytic. Plant-pathogenic fungi in the genera Phytophthora, Pythium, and Rhizoctonia constituted an increasing proportion of the fungal community isolated from seedling roots with increasing orchard block age. Bacillus megaterium and Burkholderia cepacia dominated the bacterial communities recovered from noncultivated soil and the rhizosphere of apple seedlings grown in orchard soil, respectively. Populations of the two bacteria in their respective habitats declined dramatically with increasing orchard block age. Lesion nematode populations did not differ among soil and root samples from orchard blocks of different ages. Similar changes in microbial communities were observed in response to planting noncultivated orchard soil to five successive cycles of ‘Gala’ apple seedlings. Pasteurization of soil had no effect on apple growth in noncultivated soil but significantly enhanced apple growth in third-year orchard block soil. Seedlings grown in pasteurized soil from the third-year orchard block were equal in size to those grown in noncultivated soil, demonstrating that suppression of plant growth resulted from changes in the composition of the soil microbial community. Rhizoctonia solani anastomosis group 5 (AG 5) had no effect on growth of apple trees in noncultivated soil but significantly reduced the growth of apple trees in soil from third-year orchard soil. Changes in the ability of the resident soil microflora to suppress R. solani AG 5 were associated with reductions in the relative populations of Burkholderia cepacia and Pseudomonas putida in the rhizosphere of apple.
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Schuerger, Andrew C., and William Hammer. "Use of Cross-Flow Membrane Filtration in a Recirculating Hydroponic System to Suppress Root Disease in Pepper Caused by Pythium myriotylum." Phytopathology® 99, no. 5 (May 2009): 597–607. http://dx.doi.org/10.1094/phyto-99-5-0597.
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Zoosporic pathogens in the genera Pythium and Phytophthora cause extensive root disease epiphytotics in recirculating hydroponic vegetable-production greenhouses. Zoospore cysts of Pythium myriotylum Drechsler were used to evaluate the effectiveness of cross-flow membrane filters to control pythiaceous pathogens in recirculating hydroponic systems. Four membrane filter brands (Honeycomb, Polypure, Polymate, and Absolife) were tested alone or in combination to determine which filters would effectively remove infective propagules of P. myriotylum from solutions and reduce disease incidence and severity. Zoospore cysts of P. myriotylum generally measured 8 to 10 μm, and it was hypothesized that filters with pore-sizes <5 μm would be effective at removing 100% of the infective propagules and protect pepper plants from root infection. Single-filter assays with Honeycomb and Polypure brands removed 85 to 95% of zoospore cysts when pore sizes were rated at 1, 5, 10, 20, or 30 μm. Single-filter assays of Polymate and Absolife brands were more effective, exhibiting apparently 100% removal of zoospore cysts from nutrient solutions on filters rated at 1 to 10 μm. However, plant bioassays with Honeycomb and Polymate single filters failed to give long-term protection of pepper plants. Double-filter assays with 1- and 0.5-μm Polymate filters significantly increased the protection of pepper plants grown in nutrient film technique systems but, eventually, root disease and plant wilt could be observed. Insect transmissions by shore flies were not factors in disease development. Scanning electron microscopy images of zoospore cysts entrapped on Polymate filters revealed zoospore cysts that were either fully encysted, partially encysted, or of unusually small size (3 μm in diameter). It was concluded that either the atypically small or pliable pleomorphic zoospore cysts were able to penetrate filter membranes that theoretically should have captured them.
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Barbetti, MJ, and K. Sivasithamparam. "Effects of soil pasteurization on root rot, seedling survival and plant dry weight of subterranean clover inoculated with six fungal root pathogens." Australian Journal of Agricultural Research 38, no. 2 (1987): 317. http://dx.doi.org/10.1071/ar9870317.
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Subterranean clover was exposed to two levels of inoculum of millet seed colonized by Fusarium avenaceum, Fusarium oxysporum, Phoma medicaginis, Phytophthora clandestina, Pythium irregulare, or Rhizoctonia solani within pasteurized and unpasteurized field soil from sites with (root rot site) and without (virgin site) a history of subterranean clover root rot at Augusta, W.A., with the aim of establishing their pathogenicity in the presence of other soil organisms including resident pathogens. Introduction of F. avenaceum (2.5% w/w), P. clandestina (0.5 and 2.5%), P. irregulare (0.5 and 2.5%), or R. solani (0.2 and 1.0%) increased damage to tap and lateral roots of subterranean clover in pasteurized and unpasteurized root rot and virgin soils. All fungi tested, with the exception of P. medicaginis (2.0 and 10.0%) or P. medicaginis (2.0 and 10.0%) and F. oxysporum (0.5 and 2.50%), caused reduction of seedling survival in pasteurized root rot and virgin soils respectively. When the soil was unpasteurized, all fungi except F. oxysporum (2.5%) and P. medicaginis (2.0 and 10*0%) in virgin soil, but only P. irregulare (2.5%) or R. solani (0.2 and 1.0%) in root rot soil, reduced seedling survival. In unpasteurized soils plant dry weight was reduced by P. clandestina (2.5%), P. irregulare (0.5 and 2.5%), or R. solani (0.2 and 1.0%) in root rot and virgin soils, but F. oxysporum (0.5%) reduced plant size only in the root rot soil. Within pasteurized soil all fungi, with the exception of P. medicaginis (2.0 and 10.0%) in virgin soil and F. avenaceum (2.5%), P. irregulare (0.5 and 2.5%), or R. solani (0.2%) in root rot soil, caused reduction in plant size. P. clandestina, P. irregulare or R. solani, in particular, and to a lesser extent, P. avenaceum, are capable of causing serious damage to subterranean clover in natural soil.
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Tian, Xiuling, and Youbin Zheng. "Compost Teas and Reused Nutrient Solution Suppress Plant Pathogens In Vitro." HortScience 48, no. 4 (April 2013): 510–12. http://dx.doi.org/10.21273/hortsci.48.4.510.
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In vitro testing was conducted to evaluate the inhibition potential of three compost teas (pine bark, manure, and vermicasting), Root Rescue Landscape Powder® (a mix of mycorrhizae and other beneficial microbes), waste diatomaceous earth (DE; from beer brewing), and a greenhouse nutrient solution, which had been reused for 20 years on six plant pathogens: Fusarium foetens, Rhizoctonia solani, Sclerotinia sclerotiorum, Phytophthora cryptogea, Pythium intermedium, and P. ultimum. The test materials showed in vitro inhibition on most of the test pathogens. Pine bark tea suppressed growth of all six pathogens, and inhibition exceeded 50% after 10 days of coincubation. Vermicasting tea showed over 40% inhibition against S. sclerotiorum and F. foetens; manure tea showed 42% inhibition against F. foetens; DE showed 40% inhibition against F. foetens, S. sclerotiorum, and R. solani; whereas reused greenhouse nutrient solution showed 56.7% inhibition against R. solani and 43.4% inhibition against F. foetens; Root Rescue showed 66% inhibition against P. intermedium. The results suggest that the six test materials have potential in the control of these soil- and water-borne pathogens in plant production system.
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Isutsa, Dorcas K., and Ian A. Merwin. "Malus Germplasm Varies in Resistance or Tolerance to Apple Replant Disease in a Mixture of New York Orchard Soils." HortScience 35, no. 2 (April 2000): 262–68. http://dx.doi.org/10.21273/hortsci.35.2.262.
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We tested 40 seedling lots and 17 clonal accessions—representing 941 genotypes and 19 species or interspecific hybrids of Malus—for their resistance or tolerance to apple replant disease (ARD) in a mixture of five New York soils with known replant problems. Total plant biomass, root necrosis, root-infesting fungi, and root-lesion nematode (RLN; Pratylenchus penetrans Cobb) or dagger nematode (DN; Xiphinema americanum Cobb) populations were evaluated in apple seedlings and clones grown for ≈60 days in the composite soil. In addition to phytophagous nematodes, various Pythium, Cylindrocarpon, Fusarium, Rhizoctonia and Phytophthora species were isolated from roots grown in the test soil. Plant growth response was categorized by a relative biomass index (RBI), calculated as total plant dry weight in the pasteurized field soil (PS) minus that in an unpasteurized field soil (FS), divided by PS. Nematode reproduction on each genotype was defined by a relative reproduction index (RRI), calculated as final nematode populations in roots and soil (Pf) minus initial soil populations (Pi), divided by Pi. The RBI, RRI, and other responses of accessions to ARD soil were used to rate their resistance, tolerance, or susceptibility to apple replant disease. None of the accessions was completely resistant to ARD pathogens in our test soil. Seedling accessions of M. sieversii Roem. and M. kirghisorum Ponom. appeared to have some tolerance to ARD, based upon their low RRIs and RBIs. Three clonal rootstock accessions (G.65, CG.6210, and G.30), and four other clones (M. baccata Borkh.—1883.h, M. xanthocarpa Langenf.—Xan, M. spectabilis Borkh.— PI589404, and M. mandshurica Schneid.—364.s) were categorized as tolerant to ARD. The disease response of other accessions was rated as susceptible or too variable to classify. We concluded that sources of genetic tolerance to ARD exist in Malus germplasm collections and could be used in breeding and selecting clonal rootstocks for improved control of orchard replant pathogens.
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O'Rourke, Tiernan A., Tim T. Scanlon, Megan H. Ryan, Len J. Wade, Alan C. McKay, Ian T. Riley, Hua Li, Krishnapillai Sivasithamparam, and Martin J. Barbetti. "Severity of root rot in mature subterranean clover and associated fungal pathogens in the wheatbelt of Western Australia." Crop and Pasture Science 60, no. 1 (2009): 43. http://dx.doi.org/10.1071/cp08187.
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Pasture decline is considered to be a serious challenge to agricultural productivity of subterranean clover across southern Australia. Root disease is a significant contributing factor to pasture decline. However, root disease assessments are generally carried out in the early part of the growing season and in areas predominantly sown to permanent pastures. For this reason, in spring 2004, a survey was undertaken to determine the severity of root disease in mature subterranean clover plants in pastures located in the wheatbelt of Western Australia. DNA-based soil assays were used to estimate population density in the soil of a variety of soil-borne pathogens known to commonly occur in the Mediterranean-type environments of southern Australia. The relationships between severity of disease on tap and lateral roots and root diameter, root length, nodulation, and total rainfall were determined. The survey showed, for the first time, that severe root disease is widespread in spring across the wheatbelt of Western Australia. There was a positive correlation between rainfall and tap root disease, and between tap root disease and average root diameter of the entire root system. Despite the high levels of root disease present across the sites, the DNA of most root disease pathogens assayed was detected in trace concentrations. Only Pythium Clade F showed high DNA concentrations in the soil. DNA concentrations in the soil, in particular for Phytophthora clandestina and Rhizoctonia solani AG 2.1 and AG 2.2, were higher in the smaller autumn sampling in 2006. This study suggests that the productivity of subterranean clover-based pastures is severely compromised by root rot diseases throughout the growing season in the wheatbelt of Western Australia.
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Corrêa, A. S., A. B. Rocha, S. A. Willani, J. M. Dariva, M. V. Souza, and M. G. Moraes. "Yellow Stunt, a Tobacco Disease Caused by Pythium dissotocum, in Southern Parts of Brazil." Plant Disease 95, no. 3 (March 2011): 354. http://dx.doi.org/10.1094/pdis-10-10-0759.
Full textAbstract:
Yellow stunt, an emerging disease of tobacco (Nicotiana tabacum), has become increasingly prevalent in tobacco-growing regions in southern Brazil. Major symptoms are moderate to severe stunting, yellowing of leaves, severe wilting, darkened roots, necrosis of stem tissue directly above the soil line, and plant death. Phytophthora glovera was first proposed in 1999 as the primary causal agent of yellow stunt (1), but since then, there has been no data or completion of Koch's postulates to support this. Fifty-six isolates of fungi and fungus-like organisms were obtained from stem and root samples of tobacco plants with typical symptoms of yellow stunt in the Brazilian States of Rio Grande do Sul, Santa Catarina, and Paraná during the growing seasons of 2004/05 to 2006/07. They were identified to species level by analysis of the morphological characteristics (2) and sequence of rDNA internal transcribed spacer regions 1 and 2 (ITS1 and ITS2) (3). The isolates were identified as Pythium dissotocum (29), Fusarium oxysporum (10), P. graminicola (5), Rhizoctonia solani (4), F. solani (3), P. ultimum (3), P. deliense (1), and P. inflatum (1). The ITS sequences of the 29 isolates identified as P. dissotocum were identical. The nucleotide sequence of one isolate, LFM27/2005, has been deposited in GenBank (GQ495982). Analysis of ITS sequences alone was not sufficient to differentiate this isolate from other species in the Pythium subclade B2, such as P. coloratum, P. lutarium, P. marinum, or P. diclinum. However, the combination of morphological and cultural characteristics (2) and sequence data support our identification of LFM27/2005 and similar isolates as P. dissotocum. Colonies of LFM27/2005 on cornmeal agar had filamentous sporangia and formed slightly inflated, dendroid structures. Zoospores formed at 5°C. Daily growth rate on potato carrot agar was 13 mm at 25°C. The oogonia (22 μm in diameter) were nonornamented and either intercalary or terminal. Antheridia, commonly 1 to 2 per oogonium, were sessile, born on unbranched stalks, and either monoclinous or diclinous. Aplerotic or nearly plerotic oospores measured 20 μm in diameter with a smooth wall 2.5 μm thick. Pathogenicity tests for each pathogen were performed in a greenhouse at ~24°C in pots filled with pine bark substrate infested with inoculum at the time Burley tobacco plants showed five expanded leaves. Each test consisted of five plants and was repeated three times. Inoculum for one to three isolates representative of each pathogen was prepared by growing 2-month-old cultures at 28°C in the dark for 7 days on potato dextrose agar medium overlaid with three sterile oat kernels. Noninfested oat kernels were used for control plants. Forty days after inoculation, only plants inoculated with isolates of P. dissotocum exhibited all symptoms associated with yellow stunt. P. inflatum and R. solani did not induce yellow stunt symptoms and the others induced only wilting and root rot. P. dissotocum was recovered from an inoculated, symptomatic plant, fulfilling Koch's postulates. Its morphology was identical to isolates obtained from original field samples. The results demonstrate the association of isolates of P. dissotocum with tobacco yellow stunt in Brazil. References: (1) H. D. Shew et al. Phytopathology (Abstr.) 89(suppl):S72, 1999. (2) A. J. van der Plaats-Niterink. Stud. Mycol. 21:1, 1981. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.
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AVAN, Meltem, Gülsüm PALACIOĞLU, Tülin SARIGÜL ERTEK, Yakup Zekai KATIRCIOĞLU, Harun BAYRAKTAR, Rıza KAYA, and Salih MADEN. "Sugar beet root rot caused by oomycetous pathogens in Turkey and their control by seed treatmen." TURKISH JOURNAL OF AGRICULTURE AND FORESTRY 44, no. 6 (December 8, 2020): 631–41. http://dx.doi.org/10.3906/tar-1910-55.
Full textAbstract:
The aim of this study was to determine the oomycetous pathogens causing root rot on sugar beet and test their control by seed treatment in Konya Province, Turkey. Oomycetous fungus-like pathogens of sugar beet were investigated using 866 plant samples collected at 2 growth stages, early seedling and late root, from fields in the Konya region of Turkey and 1 sample from the Thrace region. Herein, 10 oomycetous species belonging to 3 genera: Aphanomyces cochlioides, Phytophthora cryptogea, Ph. pseudocryptogea, Ph. megasperma, Ph. inundata, Pythium aphanidermatum, Py. helicoides, Py. heterothallicum, Py. sylvaticum, and Py. ultimum var. ultimum (Globisporangium ultimum var. ultimum) were discovered at various times with in the 2 growth periods, all of which were the first records for Turkey. A. cochlioides was the most serious pathogen, both in terms of its wide distribution and aggressiveness. The pathogen produced more than 90% disease severity when tested by soil infestation at the seedling stage, although it also occurred at the late root growth stage. Pythium species were also ascommon, such as A. cochlioides, the majority of which were very aggressive, producing more than 84% disease severity at the seedling stage, except for Py. aphanidermatum. Half-strength potato dextrose agar medium was found to be very useful for the isolation of all of the pathogens from the plant samples at both stages. Morphological features of all of the pathogens were abundantly produced when the pathogens were grown on amended grated carrot agar medium and culture disks of fungal growth of this medium were submerged in sterile and nonsterile soil extracts. Out of the 15 fungicide mixes tested, 2 mixes, thiram+metalaxyl+hymexazole and thiram+metalaxyl+hymexazole+ pyraclostrobin reduced seedling root rot caused by both A. cochlioides and Pythium ultimum var. ultimum, while the standard seed treatment fungicide mix of thiram+hymexazole was not effective against either of the pathogens.
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Nyoni, M., M. Mazzola, J. P. B. Wessels, and A. McLeod. "The Efficacy of Semiselective Chemicals and Chloropicrin/1,3-Dichloropropene–Containing Fumigants in Managing Apple Replant Disease in South Africa." Plant Disease 103, no. 6 (June 2019): 1363–73. http://dx.doi.org/10.1094/pdis-10-18-1844-re.
Full textAbstract:
Apple replant disease (ARD) is a biological phenomenon that is encountered when old apple orchards are replanted, resulting in tree growth and yield reductions in young trees. Three ARD orchard trials were conducted, which showed that semiselective chemicals (fenamiphos, metalaxyl, imidacloprid, and phosphonates) used independently, two fumigant formulations (33.3% chloropicrin and 60.8% 1,3-dichloropropene [Pic33-1,3D] and 57.% chloropicrin and 38% 1,3 dichloropropene [Pic57-1,3D]), and semiselective chemicals combined with Pic33-1,3D or Pic57-1,3D all contributed to significant increases in tree growth (trunk diameter and shoot length) relative to the untreated control 3 to 4 years postplanting. The treatments did not differ significantly from each other in improving tree growth. Yield was more indicative of treatment efficacy, but this varied between the three orchards. The Pic33-1,3D fumigant in combination with semiselective chemistries was the most consistent in significantly increasing cumulative yields. The Pic57-1,3D treatment was superior in increasing yields relative to the Pic33-1,3D treatment, because (i) it significantly increased cumulative yields in comparison with the Pic33-1,3D treatment in one orchard and (ii) in another orchard, a significant increase in yield was obtained with Pic57-1,3D relative to the control treatment but not with the Pic33-1,3D treatment. The quantification of ARD causative agents 20 months postplant showed that Phytophthora cactorum contributed to disease development in all three orchards; significant negative correlations existed between the quantity of P. cactorum DNA detected in tree roots and tree growth and less often, yield. In two orchards, only some of the treatments that significantly reduced the quantity of P. cactorum DNA in tree roots relative to the control also resulted in a significant increase in tree growth. Some of the aforementioned trends were also evident for Pratylenchus spp. root densities in two of the orchards. There was a significant positive correlation between P. cactorum root DNA quantities and Pratylenchus spp. root densities. Pythium spp. and “Cylindrocarpon”-like DNA quantities detected in tree roots typically were not indicative of treatment efficacy. However, a significant positive correlation existed between these two pathogen groups, suggesting complex interactions not associated with pathogen quantities per se.
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Chellemi, D. O. "Effect of urban plant debris and soil management practices on plant parasitic nematodes, Phytophthora blight and Pythium root rot of bell pepper." Crop Protection 25, no. 10 (October 2006): 1109–16. http://dx.doi.org/10.1016/j.cropro.2006.02.012.
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Johnson, Dennis A., Debra A. Inglis, and Jeffrey S. Miller. "Control of Potato Tuber Rots Caused by Oomycetes with Foliar Applications of Phosphorous Acid." Plant Disease 88, no. 10 (October 2004): 1153–59. http://dx.doi.org/10.1094/pdis.2004.88.10.1153.
Full textAbstract:
Phosphorous acid for control of tuber rots caused by Phytophthora infestans, P. erythroseptica, and Pythium ultimum was applied to foliage of potato cultivars at various application timings and rates under growing conditions in the Pacific Northwest at Othello and Mount Vernon, WA, and Bonners Ferry and Aberdeen, ID in 2001 to 2003. Efficacy was assessed by artificially inoculating harvested tubers. Mean incidence and severity of late blight tuber rot in tubers inoculated with US-8 and US-11 isolates of Phytophthora infestans usually were significantly less when the foliage from which the tubers were obtained was treated with phosphorous acid than when it was not treated at all locations. With two applications of phosphorous acid, late blight tuber rot in the tuber-resistant cv. Umatilla Russet was significantly less than for Ranger Russet. For phosphorous acid at a rate of 9.37 kg a.i./ha, late blight tuber rot control achieved with two applications at 2-week intervals was not consistently improved across locations by making an additional application 2 weeks later. In 2003, incidence and severity of late blight tuber rot did not differ significantly between the rates of 7.49 and 9.37 kg a.i./ha at both Othello and Mount Vernon. Late blight tuber rot incidence and severity were significantly less at a rate of 7.49 kg a.i./ha when the application schedule began at initial tuber bulking rather than when the first application was made 4 weeks after initial tuber bulking at Othello, but not Mount Vernon. Incidence of pink rot was significantly less in inoculated tubers from plots treated with three applications of phosphorous acid than in tubers from nontreated control plots at Mount Vernon in 2002 and 2003, Bonners Ferry in 2002, and Aberdeen in 2003. Pink rot severity was reduced significantly by both two and three phosphorous acid applications at Mount Vernon in 2002. Pink rot incidence, but not severity, was reduced significantly at all timings when either 7.49 or 9.37 kg a.i./ha was applied at Mount Vernon in 2003. Control of Pythium spp. by phosphorous acid was not evident in this study. Total tuber yield at harvest did not differ significantly among the phosphorous acid treatments and the nontreated control at Othello and Mount Vernon in 2001 and 2002.